The overall goal if this study is to evaluate median nerve somatosensory evoked potentials as an objective measure of HIV encephalopathy in children. We will examine whether, as our preliminary data strongly suggest, HIV infection in children is associated with characteristic alterations in median nerve SEPs. We will described the evolution of these alterations over time. We will determine whether median nerve SEP abnormalities are correlated with neurologic or cognitive deficits, and whether these abnormalities are detectable prior to the onset of clinically evident disease. We also will examine the relationship between development of SEP abnormalities and virologic measures of HIV infection and immune status. The study will draw on approximately 80 children born to mothers at increased risk of HIV infection and for whom detailed clinical and psychometric data will be available. An estimated 25 to 30 children infected with HIV prenatally or in the perinatal period will be compared to 50 uninfected children. The sample will be followed repeatedly up to three years of age with serial median nerve SEP studies.